链接隐式转换运算符 [英] Chaining implicit conversion operators

问题描述

我有一个类，我需要隐式转换为几个事情，中间值，例如

I've got a class which I need to implicitly convert to a few things, with intermediate values, e.g.

struct outer {
    struct inner {
        operator T() { return T(); }
    };
    operator inner() { return inner(); }
};

如果我有这种结构，总是

If I have this structure, is it always valid to do, e.g.

void f(T t);
outer o;
f(o);

推荐答案

§13.3.3.1。 2 [over.ics.user] p1

用户定义的转换序列包含初始标准转换（12.3），后跟第二个标准转换序列。

A user-defined conversion sequence consists of an initial standard conversion sequence followed by a user-defined conversion (12.3) followed by a second standard conversion sequence.

注意单数和缺少的单词序列。在隐式转换序列期间，只会考虑一个用户定义的转换。

Notice the singular and the missing of the word "sequence". Only one user-defined conversion will ever be considered during an implicit conversion sequence.

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